1. Field of the Invention
The invention relates to a signal processing apparatus which is applicable to a radio communication apparatus.
2. Description of the Prior Art
FIG. 4 shows a block diagram of a conventional signal processing apparatus as applied to a radio communication system. In FIG. 4, an analog output voice signal from a microphone 1 is converted to a digital signal in a linear codec 3. A digital signal processor (DSP ) 5 executes a coding process, a data compression process and an error correction process according to the instruction stored in a high speed PROM 24 and outputs coded data to a radio modem 6. The radio modem 6 modulates the coding data received from DSP 5 according to the instruction from a control processor 8 which controls the devices in the signal processing apparatus and transmits the modulated radio signal to the base station (not shown) via an antenna 7.
In the case of receiving the radio signal from the base station, the radio signal is input to the radio modem 6 via the antenna 7. The radio modem 6 demodulates the modulated signal and sends it to the DSP 5 . The DSP 5 decodes the coded signal according to the instruction procedure stored in the high speed PROM 24 and sends the decoded digital signal to the linear codec 3. The linear codec 3 converts the digital signal to an analog signal and sends the analog signal to a speaker 2.
FIG. 5 shows a block diagram of a second conventional signal processing apparatus which is also applied to radio communication systems. FIG. 5 is different from the FIG. 4 in that the high speed PROM 24 in FIG. 5 includes a plurality of different kinds of procedures. The DSP 5 selects one of the procedures stored in the high speed PROM 24 and controls the processes according to the selected procedure. In FIG. 5, the operation of the signal processing apparatus is otherwise the same as that of the FIG. 4. Therefore further detailed description is omitted.
As discussed above, this apparatus is designed so that the DSP 5 processes a plurality of procedures stored in the PROM 24. Since the DSP 5 operates at a high speed, the PROM 24 must also be operated at a high speed. But, the cost of the PROM 24 is very expensive because it must operate at very high speed. If the PROM 24 includes many procedures which are processed in the DSP 5, the cost will increase further.
Therefore, it is a primary object of the present invention to provide a signal processing apparatus in which a plurality of signal procedures are stored in a low cost and low speed ROM.
It is further object of the present invention to provide a signal processing apparatus in which a control processor CPU loads a plurality of signal procedures from the low speed ROM to the high speed RAM, and a digital signal processor DSP processes the signal procedures loaded in the high speed RAM.
It is still further object of the invention to provides a signal processing apparatus using a low cost memory.